1. Field of the Invention
The invention relates to the continuous casting of filament within a zone of effective vacuum. More particularly, the invention relates to an apparatus and method for continuously casting a glassy metal filament in a vacuum and continuously transporting the filament to an ambient atmosphere.
2. Description of the Prior Art
In the production of glassy alloy continuous filaments, typically an appropriate molten alloy is quenched at extreme quench rates, usually at least about 104.degree. C. per second, by extruding the molten alloy from a high speed quench surface, as is representatively shown in U.S. Pat. No. 4,142,571 for "Continuous Casting Method for Metallic Strips" issued Mar. 6, 1978 to M. Narasimhan. U.S. Pat. No. 4,221,257 for "Chill Roll Casting of Amorphous Metal Strip" issued May 13, 1980 to C. Carlson discloses additional casting apparatus comprised of a rotating annular chill roll and a flexible elastomeric belt which urges a solidified filament against the casting surface of the chill roll.
A vacuum casting device for glassy metal alloys is shown in U.S. Pat. No. 4,154,283 for "Production of Improved Metal Alloy Filaments" issued May 15, 1979 to R. Ray, et al. The vacuum casting is ordinarily accomplished by locating the casting operation in an evacuated vacuum chamber. After casting a quantity of filament, the chamber is opened to remove the filament. Such procedure is particularly tedious and inefficient because it is necessary to stop the casting operation, break the seal of the vacuum chamber to remove the filament and then reseal and restart the casting operation. Because of the very high casting speeds, the cast filament accumulates very rapidly, often piling onto the casting chamber floor and requiring frequent interruption of the casting operation to remove the filament. A winder mechanism may be located in the evacuated chamber, but this would involve pumping down a chamber large enough to contain the winder device as well as the casting equipment.
Another vacuum casting apparatus is representatively shown in U.S. Pat. No. 3,888,300 for "Apparatus for the Continuous Casting of Metals and the Like Under Vacuum" issued June 10, 1975 to Guichard, et al. The apparatus casts a metal ingot within an evacuated casting chamber and moves the cast ingot on rollers through a dynamic airlock, comprised of several suction chambers, to the atmosphere. British Pat. No. 1,387,992 "Apparatus for Continuous Casting" to W. Baker, et al. published Mar. 19, 1975 discloses a mold for casting metal formed between a pair of moving belts. The belts are cooled on their reverse sides by a coolant spray, and spaced support members support the belts.
When vacuum casting filaments at high speed, however, the filament does not reliably exit the evacuated casting chamber without experiencing entanglements and choking of the material in the exit sealing structure. In addition, the quench surface often becomes sensitized, causing the cast filament to adhere or "weld" to the quench surface instead of cleanly breaking away as ordinarily occurs when such filament is cast in an atmosphere. The welding of the filament to the quench surface can damage the casting apparatus and, along with the problem of filament choking the casting chamber exit, seriously limits the present ability to continuously cast a glassy metal filament in a vacuum at high speed.